Audio synthesis is important for a large range of applications including text-to-speech (TTS) systems and music generation. Certain existing audio generation algorithms, known as vocoders in TTS and synthesizers in music, respond to higher-level control signals to create fine-grained audio waveforms. Synthesizers have a long history of being hand-designed instruments, accepting control signals such as ‘pitch’, ‘velocity’, and filter parameters to shape the tone, timbre, and dynamics of a sound. In spite of their limitations, or perhaps because of them, synthesizers have had a profound effect on the course of music and culture in the past half century.